Develop quickly, knights before bishops; pay attention to the f7 and f2 squares; don't go chasing after a large material advantage but, destroying center pawns is ok. All of the classical aphorisims apply to the open games.
Swaping off every pawn that reaches the fourth rank is impossible and not all gambits have to be accepted. If you are not getting good positions that you like out of the opening, you should learn diffrent lines. There are a lot of them.
I like to play the open games with Black but a lot of the choices I make early in the opening are used to avoid theory. It seems that by playing this way although I don't need to memorise much the games tend to be closed rather than open.
For example in the Italian game I like to play 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.c3 Qe7. This protects e5 but usually White will either end up pushing to d5 or capturing on e5 leading to maneuvering games.
In the Ruy Lopez I play 3...g6 or 3...Nge7 which lead to about the same. I tried 3...f5 but most of the pieces were simply swapped off early in the opening leading to an endgame. 3...f5 4.Nc3 almost never occurs.
I decline just about all the gambits and meet the Vienna w/ Nf6 so I don't have to know that one.
The Scotch game/gambit I meet by taking on d4 and playing d6. This is passive but it's probably the closest thing to an open position I get out of the opening and it avoids all the theory involved with capturing pawns.
But now I'm wondering if the "proper" way to play the open games is to swap off every pawn that gets to the fourth rank and accept all the gambits. Because if White can't force Black to capture on d4 it seems like White has to play d5 and try to cramp the queenside and these aren't the types of positions I was aiming for when playing 1...e5.